The primary goal of the BLINK2 Study is to determine correlates of myopia progression using non-invasive measurement of biomarkers (choroidal thickness and intrinsically photosensitive retinal ganglion cell-mediated pupil function) and outdoor light exposure in children. If multifocal contact lenses slow the progression of myopia by 30% or more compared to single vision contact lenses during the BLINK Study, we will also answer important questions about the consequences and mechanism of the treatment effect, such as whether multifocal contact lens wear alters accommodative function and whether or not the treatment benefit is transient. Specifically, we will investigate whether myopia progression is slowed or simply delayed by multifocal contact lens wear and whether there is a ?rebound? in myopia progression, an increase in progression rate, after discontinuation of multifocal contact lenses. We will identify myopic children who will most benefit from myopia control by determining those who are most likely to progress, thereby maximizing the potential for benefit and minimizing risk. We will accomplish this goal by investigating the effect on progression of the most important ocular and environmental risk factors recently hypothesized to control eye growth. The project will collect the most extensive longitudinal dataset ever on choroidal thickness in childhood myopia. We will test the important question of whether time outdoors and light exposure influence myopia progression after onset in addition to whether these affects are mediated by intrinsically photosensitive retinal ganglion cells. If soft multifocal contact lenses show a clinically meaningful slowing of myopia progression, we will also answer important questions asked routinely by our clinical colleagues. We will know the accommodative effect of multiple years of multifocal contact lens wear in children, we will know if multifocal contact lenses slow or simply delay myopia progression, and we will know whether myopia progression increases following discontinuation of soft multifocal contact lens wear. Answers to questions addressed by this proposal could improve care for 60 million myopic children in the United States. While the consequences of ordinary myopia are rarely sight-threatening, the quality of life for myopic patients is negatively affected and the health care costs to treat myopia are high (approximately $4.6 billion in 1990). The National Eye Institute recognizes the need to evaluate the efficacy of potential treatments for delaying the onset or for slowing the progression of myopia, such as lenses that alter peripheral defocus. The BLINK2 Study seeks to maximize benefit while lowering the risk of multifocal contact lens wear for myopia control while answering important scientific and clinical questions about the consequences and mechanism of myopia progression, a problem that affects many people in the United States.